Final answer:
The total weight of the grain trader's purchase is 13000 pounds.
Step-by-step explanation:
To find the total weight of the grain trader's purchase, we need to add up the weights from each supplier. The weights are 3200 pounds, 9200 pounds, and 600 pounds. To add these together, we can simply use the arithmetic operation of addition. The total weight is 3200 + 9200 + 600 = 13000 pounds.